Reveton Trojan now encrypts images, documents and executables to thwart victims from removing the malware

A new version of the well-known police ransomware takes the unusual step of encrypting files on the infected PC, so the malware cannot be easily removed.

The ransomware warns victims that they have committed a crime, such as downloading pirated software, and their computers will remain locked until a fine is paid. The warning is dressed up to look like it's from the FBI or other law enforcement agency.

Typically, ransomware can be found and removed without paying the fraudsters. However, the latest version of the police ransomware Trojan encrypts images, documents and executables to stifle attempts to remove the malware, says a report in the AVG News and Threats blog.

"While not completely original, it is certainly unusual," Adam Wosotowsky, a security researcher for McAfee Labs, said of the anti-removal tactic. "Personally, I've cleaned some ransomware off a few machines and haven't heard of lost files due to encryption. To avoid file loss, we recommend copying personal files off the box ASAP and then re-installing Windows."

The malware does not encrypt Windows system files, so the infected PC will still work. However, the app's shenanigans do lead to a loss of some data and prevents many third-party programs from working.

Known as Reveton, the ransomware was initially found spreading in various European countries in early 2012. In May, Trend Micro found templates that indicated the authors were planning to target people in the U.S. and Canada.

In August, the FBI issued a warning saying the ransomware was spreading quickly. "We're getting inundated with complaints," Donna Gregory of the Internet Crime Complaint Center said at the time.

The malware is typically installed when victims click a link on a compromised website. Once infected, a PC immediately locks and the warning demanding payment appears.

Malicious scripts and iFrames, Web technologies used to infect PCs on compromised sites, had an 83% success rate last year, according to Cisco's 2013 Security Report, released Wednesday.

"These types of attacks often represent malicious code on 'trusted' Web pages that users may visit every day-- meaning an attack is able to compromise users without even raising their suspicion," the report says.